The invention relates to a comb filter circuit comprising a comb filter for obtaining at a first output thereof a combed high-frequency luminance signal component from a composite color television signal and at a second output thereof a combed chrominance signal component, a low-pass filter for obtaining at an output thereof a low-frequency luminance signal component from the composite color television signal, an adder circuit a first input of which is coupled to the first output of the comb filter and a second input to the output of the low-pass filter, and a detector for detecting an uncancelled chrominance signal component in the high-frequency luminance signal component, an output of the detector being coupled to a control signal input of an attenuation circuit for attenuating at least part of the high-frequency luminance signal component occurring at an output of the adder circuit at the occurrence of an uncancelled chrominance signal in said high-frequency luminance signal component.
A comb filter as described above is known from Journal of the SMPTE, January 1977, pages 1-5.
In that known circuit the detection of a spurious chrominance signal, occurring in the high frequency portion of the luminance signal during vertical transitions when the correlation between the signals in successive lines has been lost, is effected by amplifying, by means of a differential amplifier, any difference between an undelayed video signal and a video signal delayed for two line periods (2H).
The use of such a detection of the vertical transition by means of said differential amplifier is limited to the use of a configuration of the comb filter having a two-line period (2H) delay line as described in the above-mentioned SMPTE publication and is therefore not universal.